[Effect of size and number of aerobic granules on nitrification and denitrification]

Based on experimental results, a one dimension dynamic model was developed for describing the growth, maintenance and decay processes of microbes using multi substances, and consequently, the effect of size and number of aerobic granules on nitrification and denitrification were investigated. It was found that the consuming of ammonia nitrogen increased with the larger number of granules given the same biomass amount, indicating that the consumption of ammonia was dependent on the surface area of granules. The resulting amount of NO2(-) -N and NO3(-) -N was dependent not only on the amount but also on the diameter of granules, and the effect of the diameter became negligible only when the ammonia concentration was very low, suggesting the penetration depth of oxygen determines the production of NO2(-) -N and NO3(-) -N. Regarding on denitrification, for those granules with the diameter more than 1 000 microm, the denitrification increased with the increase of diameter, however, for those ones less than 1 000 microm the effect of diameter became negligible, indicating that the limitation of oxygen diffusion in granules of big granules more than 1 000 microm could help the process of denitrification.